Post by thread:[EE]: need RS232 transceiver chip

No doubt lots of you know the answer to this... I'm looking for an RS232 transceiver chip that more or less amounts to a 1488 and 1489 all on one single IC. (space is tight, and would like to avoid the need for 2 chips.) I want to stay away from the MAX232 et al because they all contain an oscillator that adds to the overall EMC noise. I already have plus/minus 12 volts on the PCB. All I have found are some obsolete parts from Mot and TI. Seems like there must be something in current production . Suggestions? -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

At 07:55 AM 7/25/00 -0700, you wrote: >No doubt lots of you know the answer to this... >I'm looking for an RS232 transceiver chip that more or >less amounts to a 1488 and 1489 all on one single IC. >(space is tight, and would like to avoid the need for 2 chips.) >I want to stay away from the MAX232 et al because they >all contain an oscillator that adds to the overall EMC >noise. I already have plus/minus 12 volts on the PCB. >All I have found are some obsolete parts from Mot and TI. >Seems like there must be something in current production . >Suggestions? > You might check what Dallas Semi has available. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

At 07:55 AM 7/25/00 -0700, you wrote: >No doubt lots of you know the answer to this... >I'm looking for an RS232 transceiver chip that more or >less amounts to a 1488 and 1489 all on one single IC. >(space is tight, and would like to avoid the need for 2 chips.) >I want to stay away from the MAX232 et al because they >all contain an oscillator that adds to the overall EMC >noise. I already have plus/minus 12 volts on the PCB. What about using a MAX232 etc anyway, but omit the switching caps, and feed the + and - 10Volt terminals with + and - 12V? Still a small internal osc running, but no power through cap switches. /Morgan -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

Any particular reason you couldn't use 3 or 4 transisters and a couple of resisters to do this? It would cost you less than nearly any single chip solution for the part, though assembly might be a tad bit more expensive. It would take up less space on a board than a 14 pin DIP, especially if you go with surface mount components. Actually, you should be able to get by with only two transisters and a few resisters. This should be cheaper than buying a seperate chip no matter what assembly technique you use. -Adam If you can't do it with duct tape, baling wire and a swiss army knife, it ain't worth doin'. Brian Aase wrote: {Quote hidden}> > No doubt lots of you know the answer to this... > I'm looking for an RS232 transceiver chip that more or > less amounts to a 1488 and 1489 all on one single IC. > (space is tight, and would like to avoid the need for 2 chips.) > I want to stay away from the MAX232 et al because they > all contain an oscillator that adds to the overall EMC > noise. I already have plus/minus 12 volts on the PCB. > All I have found are some obsolete parts from Mot and TI. > Seems like there must be something in current production . > Suggestions? > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements > > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]: PIC only [EE]: engineering [OT]: off topic [AD]: advertisements

At 07:55 AM 7/25/00 -0700, Brian Aase wrote: >No doubt lots of you know the answer to this... >I'm looking for an RS232 transceiver chip that more or >less amounts to a 1488 and 1489 all on one single IC. >(space is tight, and would like to avoid the need for 2 chips.) >I want to stay away from the MAX232 et al because they >all contain an oscillator that adds to the overall EMC >noise. I already have plus/minus 12 volts on the PCB. >All I have found are some obsolete parts from Mot and TI. >Seems like there must be something in current production . >Suggestions? I have a dumb suggestion that I have not tried out myself but *might* work: use a MAX232 but don't use the built in charge pumps. The oscillator will still run but it is the charging of the capacitors that causes most of the EMI. Leave off the 2 charge pump capacitors and feed +12V into pin 2, -12V into pin 6. You will need small bypass caps (100n) from those pins to ground, as well as from VCC (pin 16) to gnd. The neat thing is that you can delete all 4 large caps from the charge pump. Again, I have *not* tried this myself and do *not* know the consequences of power supply sequencing. But it should work and uses readily available parts. dwayne Dwayne Reid <spam_OUTdwaynerTakeThisOuTplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 16 years of Engineering Innovation (1984 - 2000) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>At 07:55 AM 7/25/00 -0700, Brian Aase wrote: ....... >>I want to stay away from the MAX232 et al because they >>all contain an oscillator that adds to the overall EMC >>noise. ....... Regarding EMI generated by these chips, I have not specifically checked the MAX232, but have extensively used the 766x-type negative voltage converter chips. Both use similar switched capacitor charge pumps. The 766x generate significant EMI - probably much more than the MAX232 since they pump more current - but if you use a ground plane under the chip, most of the noise is squelched. These facts - re EMI - are not well publicized in the datasheets AFAICT. I found this out the hard way by using a 766x [originally with no gnd plane] to drive a high sensistivity amp that was located 1" away. best regards, - Dan Michaels Oricom Technologies http://www.sni.net/~oricom ========================== -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

A cheap suggestion that has passed most tests here: LM339 with a 2.5V reference (10K+10K from 5V to GND) for receive, and pullups on the outputs. You can also use a LM393 (one pair) in the same way. The input (RxD) line is through a 4K7/47K to gnd to stay in the CMMR of the chip. Pullups depend on the speed. Peter -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Wed, 26 Jul 2000, Dan Michaels wrote: > >At 07:55 AM 7/25/00 -0700, Brian Aase wrote: > ....... > >>I want to stay away from the MAX232 et al because they > >>all contain an oscillator that adds to the overall EMC > >>noise. > ....... > Max 232 family can be supplied from +5V and other +/- source if connections to oscilators are interrupted. Without oscillator load the EMC noise must be lower than usual. All the problem may occure is to not overload the comunication pins, the chip will become hot... Vasile {Quote hidden}> > Regarding EMI generated by these chips, I have not specifically > checked the MAX232, but have extensively used the 766x-type > negative voltage converter chips. Both use similar switched > capacitor charge pumps. The 766x generate significant EMI - probably > much more than the MAX232 since they pump more current - but > if you use a ground plane under the chip, most of the noise > is squelched. > > These facts - re EMI - are not well publicized in the datasheets > AFAICT. I found this out the hard way by using a 766x [originally > with no gnd plane] to drive a high sensistivity amp that was located > 1" away. > > best regards, > - Dan Michaels > Oricom Technologies > http://www.sni.net/~oricom > ========================== > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.